Correlations of adsorption energies with physical and structural properties of adsorbate molecules

The purpose of this work is to find a suitable method to correlate Henry's law adsorption energies such as the isosteric heat or the gas-solid interaction energy. Available adsorption energies for a total of 63 gases distributed among five adsorbents-a zeolite, a silica gel, a carbon black, and two microporous carbons adsorbents were correlated with the boiling point, a critical constant ratio involving critical temperature and critical pressure, the log of the octanol-water partition coefficient, and molecular structural energy. In the structural approach each gas molecule is considered to be composed of a series of structural units that each make a fixed contribution to the total molecular adsorption energy. Multiple regression analyses were done for each of the five adsorbent systems using the four main correlation methods. The method based on the structural units of a molecule and its dipole moment was found to give a 0.99 correlation coefficient for all five gas-solid systems. This structural method was superior to correlations based on boiling points, critical constants, partition coefficients, and various combinations of other physical properties that were also examined, Since there has been a variety of interest in either predicting the energy of adsorption or extent of adsorption for specific adsorbate-adsorbent pairs, our correlation results could be useful in future quantitative structure-activity relationship (QSAR) correlations of adsorption. (C) 1997 Academic Press.